An invading army often expects victory upon reaching its target, but in this instance, the exact opposite occurs. A sudden, paralyzing terror grips the enemies of Israel the very moment they arrive at their destination. This fear is intense, manifesting as a deep shock and shuddering comparable to the sudden, sharp pains of a woman giving birth [מצודת ציון, ביאור שטיינזלץ].
The specific location where this overwhelming dread takes hold is Jerusalem [מצודת דוד]. There is profound symbolism in this setting. Exactly in the spot where these armies had plotted to carry out a massive slaughter, they are instead struck by a crippling panic. It is in this very place that they are ultimately destined to fall dead [רד״ק].
The cause of this sudden panic, especially after the enemies had already successfully gathered and organized their forces, stems from the spiritual reality of the city. The terror is brought on by the very presence of God in Jerusalem. His presence, which never moves from its place, casts a heavy awe and dread over the invading forces [אלשיך]. Struck by the sudden realization of the sheer power and greatness of the site [ביאור שטיינזלץ], the invaders completely lose their resolve. Gripped by this intense trembling, the enemies are left with no choice but to abandon their plans and flee in sheer haste [אבן עזרא].